Particle Astrophysics

1
Particle Astrophysics

• Cosmic rays
• Gamma-ray astronomy
• Neutrino astronomy

2
Multi-messenger astronomy

• Protons, g-rays, n, gravitational waves as
  probes of the high-energy universe
• Protons directions scrambled by magnetic fields
• Photons straight-line propagation but
• reprocessed in the sources
• extragalactic backgrounds absorb Eg gt TeV
• Neutrinos straight-line propagation, unabsorbed,
  but difficult to detect

3
Energetics of cosmic rays

• Energy density rE
• 10-12 erg/cm3 B2 / 8p
• Power needed rE / tesc
• galactic tesc 3 x 106 yrs
• Power 10-26 erg/cm3s
• Supernova power
• 1051 erg per SN
• 3 SN per century in disk
• 10-25 erg/cm3s
• SN model of galactic CR
• Power spectrum from shock acceleration,
  propagation

4
Problems of simplest SNR shock model

• Expect p gas ? g (TeV) for certain SNR
• Need nearby target as shown in picture from
  Nature (April 02)
• Interpretation uncertain see
• Enomoto et al., Aharonian (Nature) Reimer et
  al., astro-ph/0205256
• ? Problem of elusive p0 g-rays

• Expected shape of spectrum
• Differential index a 2.1 for diffusive shock
  acceleration
• aobserved 2.7 asource 2.1 Da 0.6 ?
  tesc(E) E-0.6
• c tesc ? Tdisk 100 TeV
• ? Isotropy problem
• Emax bshock Ze x B x Rshock
• ? Emax Z x 100 TeV with exponential cutoff of
  each component
• But spectrum continues to higher energy
• ? Emax problem

5
Spectrum normalizes atmospheric n

• GeV to TeV important for atmospheric n
• Good agreement lt 100 GeV
• AMS, BESS
• Lack of TeV data new expts
• Magnetic spectrometers
• PAMELA (2003)
• AMS on Space Station (2005)
• Meanwhile, new m-flux measurements Em gt 100 GeV
• Timmermans talk on L3C
• Somewhat below previous measurements

6
Knee of spectrum

• Differential spectral index changes at 3 x
  1015eV
• a 2.7 ? a 3.0
• Continues to 3 x 1018 eV
• Expect exp-E / Z Emax cutoff for each Z
• Fine-tuning problem
• to match smoothly a new source with a steeper
  spectrum (Axford)
• How serious is this?

7
Speculation on the knee
8
Transition to extragalactic origin?

• Ankle
• new population of particles?
• Suggestive evidence
• hardening of spectrum
• change of composition
• Measurements
• Energy
• Depth of maximum (Xmax)
• Nm / Ne

9
Air shower detectors
10
Measuring the energy of UHECR

• Ground array samples shower front
• Well-defined acceptance
• Simulation relates observed ground parameter to
  energy
• Fluorescence technique tracks shower profile
• Track-length integral gives calorimetric measure
  of energy
• Xmax sensitive to primary mass Xmax L ln(E0/A)

11
Xmax vs Energy

• Protons penetrate deeper into atmosphere
• Heavy nuclei develop higher up
• Plot shows a summary of data over 5 decades
• Several techniques
• Some dependence on models of hadronic
  interactions (R. Engels talk)

12
Xmax vs Energy

• Lines indicate trend of data
• Light to heavy above the knee (1016 ? 1017 eV)
• Heavy to light at the ankle (1018 ? 1019 eV)
• AGASA looks at m/e ratio in shower front and sees
  no evidence for change of composition at the ankle

13
Energy of extragalactic component

• Energy density
• ?CR gt 2 x 10-19 erg/cm3
• Estimate requires extrapolation of UHECR to low
  energy
• Power required
• gt?CR/1010 yr
• 1.3 x 1037 erg/Mpc3/s
• 10-7 AGN/Mpc3
• Need gt1044 erg/s/AGN
• 1000 GRB/yr
• Need gt3 x 1052 erg/GRB

14
Highest energy cosmic rays

• GZK cutoff?
• Expected from energy loss in 2.7o background for
  cosmological sources

Attenuation length in microwave background
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Compare AGASA HiRes
Ground array
Fluorescence detector

• Exposure (103 km2 yr sr)
• AGASA 1.3
• HiRes (mono) 2.2
• Number events gt1020
• AGASA 10 (2?)
• HiRes (mono) 2?
• Both detectors have energy-dependent acceptance
  (different)
• Need more statistics and stereo results

16
Models of UHECR
( Incomplete list-- Refs. in written version )

• Bottom up (acceleration)
• Jets of AGN
• External
• Internal (PIC models)
• GRB fireballs
• Accretion shocks in galaxy clusters
• Galaxy mergers
• Young SNR
• Magnetars
• Observed showers either protons (or nuclei)

• Top-down (exotic)
• Radiation from topological defects
• Decays of massive relic particles in Galactic
  halo
• Resonant neutrino interactions on relic ns
  (Z-burst)
• Large fraction of g-showers (especially if local
  origin)

If no cutoff, require a significant
contribution from nearby sources. Local
overdensity of galaxies is insufficient if UHECR
source distribution follows distribution of
galaxies.
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Biggest event
Flys Eye, Ap. J. 441 (1995) 295

• Comparison to
• Proton showers
• Iron showers
• g showers

18

• Most of shower absorbed, mostly
• muons survive to the ground

• Heavy primaries produce more m

• Incident photons produce few m

• Analysis of vintage (aged 25 yrs)
• data from Haverah Park array
• possible with modern simulation
• tools

• Results place interesting limits
• limits on Top-Down models

• UHE events from decaying,
• massive relics accumulated in
• the Galactic halo would be mostly
• photon-induced showers. Such
• models are therefore disfavored
• Similar limit on g/p from AGASA

19
Auger hybrid event
Fluorescence detector view
Engineering Array SD with 40 modules 100
km2 viewed by fluorescence detector. Now
operating in Argentina. 100 more tanks running
in 2003.
Surface detector view
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Active Galaxies Jets
Radio Galaxy 3C296 (AUI, NRAO). --Jets extend
beyond host galaxy.
Drawing of AGN core
VLA image of Cygnus A
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Egret blazars

• Blazars are AGN with jet
• illuminating observer.
• Two-component spectra
• interpreted as synchrotron
• radiation (low energy) plus
• inverse Compton generated
• by high-energy electrons
• accelerated to high energy
• in relativistic jets (G 10).
• A few nearby blazars have
• spectra extending to gt TeV
• observed by ground-based
• Imaging Atmospheric
• Cherenkov Telescopes (IACT).

22
AGN Mulitwavelength observations

• SSC, EC, PIC models
• 1st peak from electron synchrotron radiation
• 2nd peak model-dependent predict n flux if PIC
• Interpretation complex
• Sources variable
• Locations of peaks depend on source-- factor of
  gt100 range of peak energy
• New detectors (GLAST, HESS, MAGIC, VERITAS) will
  greatly expand number, variety of sources

23
Solar arrays for g-ray astronomy explore down to
100 GeV
CELESTE, STACEE in operation
Celeste
STACEE
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TeV g Blazars

• Five detected
• Mrk 421 (Z 0.031)
• Mrk 501 (Z 0.034)
• 1ES2344514 (Z 0.044)
• 1H1426428 (Z 0.129)
• 1ES1959650 (Z 0.048)
• Whipple, IAU Circular 17 May 2002
• Emax vs Z probes era of galaxy-formation through
  IR background

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Blazar spectra at high energy

• Mrk 421 Mrk 501,
• Cutoffs
• Intrinsic?
• Effect of propagation?
• Variable sources
• Low intensity softer spectrum
• Interpretation under debate
• Need more observations of more sources at various
  redshifts

both at z .03
HEGRA plots from Aharonian et al.
astro-ph/0205499. Different Ecut of 421 and 501
suggest cutoffs are intrinsic. Comparable
analysis of Whipple extends to lower energy.
Seeing comparable cutoffs, they suggest effect
is due to propagation. Krennrich et al., Ap.J.
560 (2002) L45
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Sky map from the Milagro detector
Milagro is a compact air shower detector that
uses a 60 x 80 m water Cherenkov pool covered
and surrounded by air shower detectors.
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Detectors for gamma-ray astronomy
Egret 1991-2000
Presently running
Multiple telescope arrays for stereo operation
Future
AMSSecondary Mode of operation
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Gamma-ray astronomypresent and future
A. Morselli, S. Ritz
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H.E.S.S.

• First events
• June, 2002

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Gamma-ray bursts

• Cosmological bursts
• Studies of afterglows (ROTSE, Beppo-Sax ID)
  determine Z 1
• Hypernova or coalescing compact objects
• Relativistic jets (G 100)
• Acceleration at internal shocks
• Possible acceleration when jets interact with
  environment
• Are GRBs sufficiently powerful and numerous to
  supply the UHECRs?
• This question currently under debate
• Soft Gamma Repeaters
• Galactic magnetars, B 1015 G
• Satisfy ebcBR gt 1020 eV
• SWIFT to be launched in 2003

31
Neutrino Astronomy
Skymap of upward events

• SN1987A, Solar n
• High-energy n astronomy
• DUMAND
• Baikal, AMANDA
• Currently running
• Atmospheric ns detected
• Limits on point sources, diffuse high-energy ns,
  WIMPs, monopoles
• Km3-scale projects getting underway

AMANDA astro-ph/0205019
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South Pole
Dark sector
Skiway
AMANDA
Dome
IceCube
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Expected sensitivity AMANDA 97-02 data
southern sky
northern sky
m ? cm-2 s-1
4 years Super-Kamiokande
10-14
170 days AMANDA-B10
8 years MACRO
10-15
declination (degrees)
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Development of kilometer-scale n telescopes ...
complementary sky-views and techniques
IceCube in Antarctic ice
Antares Nemo, Nestor
Km3 in the Mediterranean Sea
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Skymaps and exposure to gamma-ray bursters
BATSE 2706 GRBs Beppo-SAX 126 GRBs
Plot by Teresa Montaruli is grey-scale image of
sky coverage for upward events (black no
coverage, white full coverage). Applies to
Enlt PeV when Earth needed to shield against
downward events.
36
Neutrino flavor ID

• P ? p ? nm m ? e ne nm
• nm ne nt 2 1 0 at production
• oscillations give 1 1 1 at Earth
• En lt PeV
• nm upward m track
• ne, nt cascades
• En gt PeV
• Rt 50 m / Et (PeV)
• nt gives double bang or lollipop signature
  (large cascade preceded or followed by a long,
  cool track)

37
n Propagation in the Earth

• Lower hemisphere 50 opaque for En PeV
• Regeneration of nt
• nt ? t ? n ? cascade
• Look for excess of upward cascades between 0.1
  and 10 PeV
• For En gt PeV can use downward neutrinos as well
  as upward

38
Expected signals in km3

• Possible point sources
• Galactic
• SNR 0 - 10 events / yr
• m-quasars 0.1 - 5 / burst
• 100 / yr, steady source
• Extra-galactic
• AGN jets 0-100 / yr
• GRB precursor (100 s)
• 1000 bursts / yr
• 0.2 events / burst
• GRB jet after breakout
• smaller mean signal / burst
• Nearby bursts give larger signal in both cases
  

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Proposed detectors for En EeV

• Air shower arrays
• Signature Horizontal EAS
• Veff 10 m.w.e. x area
• e.g. 30 Gt for Auger
• (Acceptance 30 x larger for nt in Auger)
• gt1000 Gt for EUSO, OWL
• Radio detectors
• RICE (antennas in S.P. ice)
• ANITA (antennas on long-duration Antarctic
  balloon)
• SALSA (in salt domes)
• GLUE (Goldstone antenna search for n interact in
  moon)

• Note despite larger Veff , rates may be
  comparable or smaller than in Km3 detectors with
  lower Ethreshold by an amount depending on source
  spectrum

40
Summary

• Need more statistics and cross-calibration for
  ultra-high energy cosmic rays
• Expect another leap in g-astronomy with GLAST and
  new ground telescope arrays
• Kilometer-scale neutrino telescopes to open new
  window on energetic Universe
• Many active and new experiments in this rapidly
  developing field -- stay tuned!

41
Diffuse galactic secondaries

• p gas ? p0, p/-, antiprotons
• p0 ? g g p/- ? n
• Hard g-spectrum suggests some
• contribution from collisions at sources

Phys.Rev.Lett. 88 (2002) 051101
42
Lessons from the heliosphere

• ACE energetic particle fluences
• Smooth spectrum
• composed of several distinct components
• Most shock accelerated
• Many events with different shapes contribute at
  low energy (lt 1 MeV)
• Few events produce 10 MeV
• Knee Emax of a few events
• Ankle at transition from heliospheric to galactic
  cosmic rays

R.A. Mewaldt et al., A.I.P. Conf. Proc. 598
(2001) 165
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Heliospheric cosmic rays

• ACE--Integrated fluences
• Many events contribute to low-energy heliospheric
  cosmic rays
• fewer as energy increases.
• Highest energy (75 MeV/nuc) is dominated by
  low-energy galactic cosmic rays, and this
  component is again smooth
• Beginning of a pattern?

R.A. Mewaldt et al., A.I.P. Conf. Proc. 598
(2001) 165
44
Reconstruction Handles for neutrino astronomy
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Energy resolution

• Systematics
• DE / E 20 for 1018 eV
• By cross-calibrating different detectors
• By using different models
• By comparing spectra of different experiments and
  techniques
• Fluctuations in Smax
• underestimate E if measured at max,
• overestimate if past max

46
GRB model
Bahcall Waxman, hep-ph/0206217

• Assumes E-2 spectrum at source
• 2.5 x 1053 erg/GRB
• 0.4 x 1037 erg/Mpc3/s
• Evolution like star-formation rate
• GZK losses included
• Galactic? extragalactic transition 1019 eV

47
AGN model
Curves 2,3,4 with local overdensity of sources.
2 is observed overdensity.
Berezinsky et al., hep-ph/0204357

• Assumes two-component spectra
• steep at high energy
• 1039 erg/Mpc3/s
• note high value
• Evolution, GZK losses
• Compares to AGASA data, cannot explain 5 events
• Transition to extragalactic at low energy

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